Earlier this year I purchased a 2006 370SS with 496 HO's. Starboard engine at cruise (3500 to 4000 rpms) is running around 163 degrees engine temp with 25 to 30 psi H2O pressure. Port was running around 175 degrees at 17 to 19 psi H2O pressure. Installed a Hardin pump on the Port engine hoping the H2O pressure would go up and engine temp would lower. The H2O pressure did raise when at idle but once it hit the 17-19 psi mark when getting up to speed that is where it would stay regardless of rpm's at cruising speeds. Engine temp stayed around 175 degrees. My thought would be if there were a restriction somewhere after the raw water pump I would be getting a higher H2O pressure reading, so I'm guessing there might be a restriction somewhere in the pickup line? If so where should I start looking? Any thoughts or opinions?

Did the impeller on your old pump come apart? If so there may be a blockage from old pieces - you will have to back flush in order to get them out.

A restriction to the inlet of the pump would cause lower pressure.

Are you getting any unexplained water in the bilge? Perhaps your air drain actuators springs are aging, and allowing water to purge out of the system at speed.
http://www.offshoreonly.com/forums/d...-fittings.html

Also, do you have a fresh water flush fitting? Some manufacturers installed that type of system with a Tee into the system that has a spring and a check ball. That unit can get gummed up with seaweed/debris and restrict water flow, especially at higher speeds.

Do you have DWP or LWP drives? You can use a long drill bit BY HAND to twist into the Lower Water Pickups to bring out any debris, perhaps wood splinters that may be in the holes.

Before I relocated the boat I had a mechanic backflush both engines just in case because the previous owner had problems with zebra mussels a few years ago. Doesn't mean it got done but they told me everything checked out ok. New impellers were installed after the backflushing and were in good condition when the Hardin pump was installed.

Sydwayz - yes I am getting unexplained water in the bilge under the port side engine. I'm guessing I can check for water leaking out when running at cruise?
Not sure if I have a fresh water flush fitting, boat was only in fresh water, I will have to check.
Also not sure on DWP vs LWP, I will have to look. The drives were removed and check out this spring and I was told everything looked good.

I'm assuming you have the boat moored in the water, not on a trailer or lift.
Tough to do on that boat, but open the hatch and have someone rev it up to 2500 or so in neutral, briefly, while you are peering under the engine. You may see water spraying downward at either the forward port side of the engine, or aft starboard side, which is where the two air drain actuators are located. Follow the white & green air lines, and you will see where to be looking.

And definitely order up some new Heat Exchanger end cap gaskets, open the H/Es, flush them out and replace the gaskets. If the boat had Zebra muscle issues, and you don't know the history of when the last time the H/Es were serviced, this needs to be done.

Sydwayz - The boat is sitting on a lift if that makes a difference on how to test the actuators, or should I just lower and test sitting in the water?
When the engines were backflushed the heat exchangers were removed to check for mussels, non were found and the gaskets were replaced when put back together.

Actually, being on the lift is going to make it easier to check all of your pickup holes on the drive, as long as you have a walk up platform under the drives, or if you can float under them on a rowboat/raft/whatever.

And either lower the boat completely in the water, or at least enough that you fan fire it up and have it not float out on you; but you still have your water pickups as far underwater as possible. IF you have DWP drives, you must have the lower and the upper holes underwater.